scholarly journals Composite Synoptic-Scale Environments Conducive to North American Polar–Subtropical Jet Superposition Events

2020 ◽  
Vol 148 (5) ◽  
pp. 1987-2008 ◽  
Author(s):  
Andrew C. Winters ◽  
Daniel Keyser ◽  
Lance F. Bosart ◽  
Jonathan E. Martin
Keyword(s):  
North American ◽  
Diabatic Heating ◽  
High Impact ◽  
Synoptic Scale ◽  
Event Type ◽  
Latitude Band ◽  
Dynamic Mechanisms ◽  
Subtropical Jet ◽  
Frequent Event ◽  
High Impact Weather

Abstract A polar–subtropical jet superposition represents a dynamical and thermodynamic environment conducive to the production of high-impact weather. Prior work indicates that the synoptic-scale environments that support the development of North American jet superpositions vary depending on the case under consideration. This variability motivates an analysis of the range of synoptic–dynamic mechanisms that operate within a double-jet environment to produce North American jet superpositions. This study identifies North American jet superposition events during November–March 1979–2010 and subsequently classifies those events into three characteristic event types. “Polar dominant” events are those during which only the polar jet is characterized by a substantial excursion from its climatological latitude band, “subtropical dominant” events are those during which only the subtropical jet is characterized by a substantial excursion from its climatological latitude band, and “hybrid” events are those characterized by a mutual excursion of both jets from their respective climatological latitude bands. The analysis indicates that North American jet superposition events occur most often during November and December, and subtropical dominant events are the most frequent event type for all months considered. Composite analyses constructed for each event type reveal the consistent role that descent plays in restructuring the tropopause beneath the jet-entrance region prior to jet superposition. The composite analyses further show that surface cyclogenesis and widespread precipitation lead the development of subtropical dominant events and contribute to jet superposition via their associated divergent circulations and diabatic heating, whereas surface cyclogenesis and widespread precipitation tend to peak at the time of superposition and well downstream of polar dominant events.

scholarly journals Nonlinear Characteristics of Ensemble Perturbation Evolution and Their Application to Forecasting High-Impact Events

2013 ◽  
Vol 28 (6) ◽  
pp. 1353-1365 ◽  
Author(s):  
Brian C. Ancell
Keyword(s):  
Weather Prediction ◽  
Ensemble Member ◽  
High Impact ◽  
Synoptic Scale ◽  
Wind Speeds ◽  
Weather Events ◽  
Ensemble Mean ◽  
High Impact Weather ◽  
The Mean ◽  
Impact Events

Abstract Ensemble forecasting is becoming an increasingly important aspect of numerical weather prediction. As ensemble perturbation evolution becomes more nonlinear as a forecast evolves, the ensemble mean can diverge from the model attractor on which ensemble members are constrained. In turn, the ensemble mean can become increasingly unrealistic, and although statistically best on average, it can provide poor forecast guidance for specific high-impact events. This study uses an ensemble Kalman filter to investigate this behavior at the synoptic scale for landfalling midlatitude cyclones. This work also aims to understand the best way to select “best members” closest to the mean that both behave realistically and possess the statistically beneficial qualities of the mean. It is found that substantial nonlinearity emerges within forecast times of a day, which roughly agrees with previous research addressing synoptic-scale nonlinearity more generally. The evolving nonlinearity results in unrealistic behavior of the ensemble mean that significantly underestimates precipitation and wind speeds associated with the cyclones. Choosing a single ensemble member closest to the ensemble mean over the entire forecast window provides forecasts that are unable to produce the relatively small errors of the ensemble mean. However, since different ensemble members are closest to the ensemble mean at different forecast times, the best forecast is composed of different ensemble members throughout the forecast window. The benefits and limitations of applying this methodology to improve forecasts of synoptic-scale high-impact weather events are discussed.

Weather regimes in South East Asia: Sub-seasonal predictability of the regimes and the associated high impact weather  

2021 ◽  
Author(s):  
Paula Gonzalez ◽  
Emma Howard ◽  
Simon Thomas ◽  
Thomas Frame ◽  
Oscar Martinez-Alvarado ◽  
...  
Keyword(s):  
East Asia ◽  
Large Scale ◽  
High Impact ◽  
Lead Times ◽  
South East Asia ◽  
Synoptic Scale ◽  
Seasonal Predictability ◽  
Weather Regimes ◽  
Predictive Skill ◽  
High Impact Weather

<div> <p>This work considers the sub-seasonal predictability of two sets of weather regimes for South East Asia: a two-tiered assignment, that first considers large-scale patterns and then assigns synoptic-scale regimes, and a flat classification, which only considers the synoptic scale. In the two-tiered approach, the tier 1 large-scale regimes, which capture ENSO and seasonal variations, are each partitioned into South East Asia regional clusters that capture synoptic variability.   </p> </div><div> <p>The sub-seasonal predictability of both the standard and tiered regimes is assessed using UKMO GloSea5 hindcasts and forecasts for lead times of up to 5 weeks. We find that the GloSea5 system presents an accurate representation of the regimes’ climatology and a good level of skill for their assignment. Nonetheless, the predictability depends on the specific regimes and some significant forecast drifts are also identified. Additionally, the predictive skill of high impact precipitation events obtained statistically from the prediction of the regimes is assessed and compared with the probabilistic precipitation forecasts of the GloSea5 ensemble.    </p> </div><div> <p>A description of the regime classification methodology and their connections to seasonal and synoptic phenomena will be discussed in a separate presentation, titled “Weather regimes in South East Asia: connections with synoptic phenomena and high impact weather” and presented by Emma Howard. </p> </div>

The Role of a Polar/Subtropical Jet Superposition in the May 2010 Nashville Flood

2014 ◽  
Vol 29 (4) ◽  
pp. 954-974 ◽  
Author(s):  
Andrew C. Winters ◽  
Jonathan E. Martin
Keyword(s):  
Deep Convection ◽  
Moisture Flux ◽  
High Impact ◽  
Subtropical Jet ◽  
Weather Events ◽  
Two Component ◽  
High Impact Weather ◽  
Ageostrophic Circulation ◽  
Tropical Moisture

Abstract Contributions to the increased poleward moisture flux that characterized the second day of the 1–3 May Nashville, Tennessee, flood of 2010 are examined from the perspective of polar and subtropical jet superposition and its influence on the secondary ageostrophic circulation. Employing the Sawyer–Eliassen circulation equation, the analysis reveals that the poleward moisture flux attributed to the jet increased nearly 120% prior to the second day of the event in response to the superposed jet’s ageostrophic circulation, helping to further fuel the production of heavy rainfall. The full Sawyer–Eliassen circulation associated with the superposed jet is further partitioned into its geostrophic and diabatic components. The geostrophic forcing drove midtropospheric ascent that fueled the production of deep convection and the record rainfall. The diabatic component, through forcing lower-tropospheric ascent and vigorous lower-tropospheric poleward moisture flux, provided the link between the tropical moisture and the deep convective environment. Since superposed jets, by their nature, develop on the poleward edge of the tropical or subtropical air, it is suggested that such a mutually reinforcing interaction between these two component forcings of the secondary circulation may routinely characterize the involvement of superposed jet structures in high-impact weather events.

Unsteady vortex behavior in the Asian monsoon anticyclone

2021 ◽  
Author(s):  
Leong Wai Siu ◽  
Kenneth Bowman
Keyword(s):  
Vortex Shedding ◽  
Diabatic Heating ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Synoptic Scale ◽  
Single Vortex ◽  
Summer Circulation ◽  
Upper Troposphere ◽  
Subtropical Jet ◽  
Heat Released

<p>The Asian monsoon anticyclone (AMA), which is primarily driven by the latent heat released by monsoon precipitation, is one of the dominant features of the Northern Hemisphere summer circulation in the upper troposphere and lower stratosphere. Due to variations in the diabatic heating, interactions with Rossby waves propagating along the subtropical jet, and internal dynamics within the anticyclone, the circulation of the AMA is unsteady. Here we use the ERA-Interim dataset and trajectories computed with ERA-Interim winds to show that the AMA contains two or three distinct synoptic-scale subvortices 69% of the time, while a single circulation center is present only 23% of the time. More than three simultaneous subvortices are uncommon. Observed behaviors of the subvortices include 1) splitting of a single vortex into two vortices; 2) merger of two vortices into a single vortex; 3) vortex shedding in the eastward direction; 4) vortex shedding in the westward direction; and 5) formation, movement, and dissipation of a vortex. The evolution of the subvortices is closely tied to stirring and transport.</p>

scholarly journals Unsteady Vortex Behavior in the Asian Monsoon Anticyclone

2020 ◽  
Vol 77 (12) ◽  
pp. 4067-4088
Author(s):  
Leong Wai Siu ◽  
Kenneth P. Bowman
Keyword(s):  
Vortex Shedding ◽  
Diabatic Heating ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Synoptic Scale ◽  
Single Vortex ◽  
Summer Circulation ◽  
Upper Troposphere ◽  
Subtropical Jet ◽  
Heat Released

AbstractThe Asian monsoon anticyclone (AMA), which is primarily driven by the latent heat released by monsoon precipitation, is one of the dominant features of the Northern Hemisphere summer circulation in the upper troposphere and lower stratosphere. Due to variations in the diabatic heating, interactions with Rossby waves propagating along the subtropical jet, and internal dynamics within the anticyclone, the circulation of the AMA is unsteady. Here we use the ERA-Interim dataset and trajectories computed with ERA-Interim winds to show that the AMA contains two or three distinct synoptic-scale subvortices 69% of the time, while a single circulation center is present only 23% of the time. More than three simultaneous subvortices are uncommon. Observed behaviors of the subvortices include 1) splitting of a single vortex into two vortices; 2) merger of two vortices into a single vortex; 3) vortex shedding in the eastward direction; 4) vortex shedding in the westward direction; and 5) formation, movement, and dissipation of a vortex. The evolution of the subvortices is closely tied to stirring and transport.

scholarly journals A methodology to conduct wind damage field surveys for high-impact weather events of convective origin

2020 ◽  
Vol 20 (5) ◽  
pp. 1513-1531 ◽  
Author(s):  
Oriol Rodríguez ◽  
Joan Bech ◽  
Juan de Dios Soriano ◽  
Delia Gutiérrez ◽  
Salvador Castán
Keyword(s):  
Field Studies ◽  
High Impact ◽  
Strong Wind ◽  
Field Surveys ◽  
Weather Events ◽  
Straight Line ◽  
High Impact Weather ◽  
Strong Winds ◽  
Wind Events ◽  
The One

Abstract. Post-event damage assessments are of paramount importance to document the effects of high-impact weather-related events such as floods or strong wind events. Moreover, evaluating the damage and characterizing its extent and intensity can be essential for further analysis such as completing a diagnostic meteorological case study. This paper presents a methodology to perform field surveys of damage caused by strong winds of convective origin (i.e. tornado, downburst and straight-line winds). It is based on previous studies and also on 136 field studies performed by the authors in Spain between 2004 and 2018. The methodology includes the collection of pictures and records of damage to human-made structures and on vegetation during the in situ visit to the affected area, as well as of available automatic weather station data, witness reports and images of the phenomenon, such as funnel cloud pictures, taken by casual observers. To synthesize the gathered data, three final deliverables are proposed: (i) a standardized text report of the analysed event, (ii) a table consisting of detailed geolocated information about each damage point and other relevant data and (iii) a map or a KML (Keyhole Markup Language) file containing the previous information ready for graphical display and further analysis. This methodology has been applied by the authors in the past, sometimes only a few hours after the event occurrence and, on many occasions, when the type of convective phenomenon was uncertain. In those uncertain cases, the information resulting from this methodology contributed effectively to discern the phenomenon type thanks to the damage pattern analysis, particularly if no witness reports were available. The application of methodologies such as the one presented here is necessary in order to build homogeneous and robust databases of severe weather cases and high-impact weather events.

scholarly journals Influential Role of Moisture Supply from the Kuroshio/Kuroshio Extension in the Rapid Development of an Extratropical Cyclone

2015 ◽  
Vol 143 (10) ◽  
pp. 4126-4144 ◽  
Author(s):  
Hidetaka Hirata ◽  
Ryuichi Kawamura ◽  
Masaya Kato ◽  
Taro Shinoda
Keyword(s):  
Diabatic Heating ◽  
Rapid Development ◽  
Kuroshio Extension ◽  
Lower Troposphere ◽  
Active Role ◽  
Conveyor Belt ◽  
Synoptic Scale ◽  
Warm Front ◽  
The Kuroshio

Abstract This study focused on an explosive cyclone migrating along the southern periphery of the Kuroshio/Kuroshio Extension in the middle of January 2013 and examined how those warm currents played an active role in the rapid development of the cyclone using a high-resolution coupled atmosphere–ocean regional model. The evolutions of surface fronts of the simulated cyclone resemble the Shapiro–Keyser model. At the time of the maximum deepening rate, strong mesoscale diabatic heating areas appear over the bent-back front and the warm front east of the cyclone center. Diabatic heating over the bent-back front and the eastern warm front is mainly induced by the condensation of moisture imported by the cold conveyor belt (CCB) and the warm conveyor belt (WCB), respectively. The dry air parcels transported by the CCB can receive large amounts of moisture from the warm currents, whereas the very humid air parcels transported by the WCB can hardly be modified by those currents. The well-organized nature of the CCB plays a key role not only in enhancing surface evaporation from the warm currents but also in importing the evaporated vapor into the bent-back front. The imported vapor converges at the bent-back front, leading to latent heat release. The latent heating facilitates the cyclone’s development through the production of positive potential vorticity in the lower troposphere. Its deepening can, in turn, reinforce the CCB. In the presence of a favorable synoptic-scale environment, such a positive feedback process can lead to the rapid intensification of a cyclone over warm currents.

A role of high impact weather events in waterborne disease outbreaks in Canada, 1975 – 2001

2006 ◽  
Vol 16 (3) ◽  
pp. 167-180 ◽  
Author(s):  
Kate M. Thomas ◽  
Dominique F. Charron ◽  
David Waltner-Toews ◽  
Corinne Schuster ◽  
Abdel R. Maarouf ◽  
...  
Keyword(s):  
Disease Outbreaks ◽  
High Impact ◽  
Waterborne Disease ◽  
Weather Events ◽  
High Impact Weather
Sign in / Sign up

Export Citation Format

Share Document